The Pathology Repository Center and the eight Regional Centers are headed by pathologists who have specialized in the diagnosis and study of neoplastic diseases of the lymphoid system and are making a joint effort to improve and refine the criteria for diagnosis and classification of these neoplastic diseases, thus assuring the validity of the therapeutic results obtained by their clinical colleagues engaged in therapeutic clinical studies. The Pathology Panel and Repository Center for Lymphoma Clinical Studies has five major objectives which are closely interrelated; (1) Maintenance of a Patholoy Repository Center and eight Regional Centers for lymphoma Clinical studies conducted by NIH supported cooperative groups and of a pathology reference file for clinical study of Hodgkin's disease supported by USPHS Grant 5R10 CA13607; (2) Testing of the new working formulation of non-Hodgkin's lymphoma for clinical usage recommended by an expert international panel for reproducibility and clinical relevance; (3) Education of pathologists who are responsible for entry diagnoses of the cooperative protocol studies in an effort to increase the quality of their diagnoses and thereby minimize entry of any patients into protocols to which they do not belong; (4) Furnishing research support for clinical cooperative groups engaged in lymphoma clinical studies; (5) Utilization of histopathologic material stored in the Repository Center for ancillary research projects closely related to the primary aim.